Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$96.76	13.112%	$109.4472	$109.45	$109.45	$109.40
Purchase #2	$36.27	3.505%	$37.5413	$37.54	$37.55	$37.50
Purchase #3	$166.81	7.804%	$179.8279	$179.83	$179.85	$179.80
Purchase #4	$14.50	9.149%	$15.8266	$15.83	$15.85	$15.80
Purchase #5	$240.29	13.844%	$273.5557	$273.56	$273.55	$273.60
Purchase #6	$36.94	12.675%	$41.6221	$41.62	$41.60	$41.60
Purchase #7	$98.64	11.349%	$109.8347	$109.83	$109.85	$109.80
7 purchase totals =	$690.21		$767.6555	$767.66	$767.70	$767.50